JP2001294920A - Method for producing reduced iron - Google Patents

Abstract

PROBLEM TO BE SOLVED: To establish a method for stably and efficiently performing the formation of a raw material body, a drying and a solid-reduction of the body by solving such problems caused by using the large diameter body as the non- uniform formation and drying of the body, the low strength, and the shortage of heat-transfer at the heating and reducing time, when a reduced iron is produced by heating and solid-reducing the mixture containing iron oxide and carbonaceous reducing agent. SOLUTION: The raw material body with the small diameter desirably <=10 mm and further, desirably <6 mm, is used and the solid-reduction is performed by charging the bodies on a shifting furnace hearth so as to be stacked as layers and heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in technology for obtaining solid reduced iron by heating and reducing iron oxide such as iron ore with a carbonaceous reducing agent such as coke, and more particularly, to an improvement in the technology included in iron ore and the like. The present invention relates to an improved method for efficiently producing solid reduced iron by efficiently reducing solid oxide by simple treatment.

[0002]

2. Description of the Related Art As a method for producing reduced iron similar to the present invention, many methods are known as follows.

JP-A-11-337264 discloses that reduced iron is produced by forming a raw material powder containing an iron oxide source such as iron ore and coke into pellets, and heating and reducing the raw pellets. A method is disclosed. According to this publication, a raw material powder containing an iron oxide source and coke is molded, and when the raw material powder is heated and reduced to produce reduced iron, the raw material compact is charged into a heating reduction furnace in an undried state. Discloses a method of performing successive drying and heat reduction,
Although this method has the advantage of omitting the equipment and time required for drying the raw material molded body, it requires a pre-tropical zone that also serves as drying before the heat reduction zone, so the entire furnace must be large. I can't get it. Moreover, in order to prevent the flow of the high-temperature gas from the heating reduction zone in the pre-tropical direction, for example, a shielding member such as a curtain wall must be provided, which causes a problem that the structure of the furnace becomes complicated and the equipment cost increases. .

Japanese Patent Laid-Open Publication No. Hei 10-30106 discloses a method in which the surface of a raw material layer placed on a hearth is shaped like a ridge and the surface area of the raw material layer is increased to increase the heating efficiency. Have been. However, the raw material pellets disclosed in this publication have a medium to large particle size of 10 to 20 mm, have a low rate of heat transfer of the burner heating or radiant heat to the inside of the pellet, and form ridges. Even
The pellets are stacked in several layers, and a sufficient heat transfer effect cannot always be obtained. This publication also recommends that the ridge be plowed in the middle of the heat reduction to increase the heating efficiency, but plowing the laminated portion of the medium to large particle size pellets may damage the pellets. And lower the yield of reduced iron.

Japanese Patent Laid-Open Publication No. Hei 10-306304 discloses a method of supplying raw material powder while forming irregularities on a hearth. However, according to this method, the maximum deposition thickness of the raw material is very thick, 120 mm, and the raw material powder is only a mixture of the iron oxide source and the carbonaceous material. The heat property and the reduction reactivity are considerably inferior to the case where a molded body is used.

JP-A-11-193423: This publication discloses a method for producing reduced iron by supplying pellets containing an iron oxide source and a carbon material to a rotary hearth-type reduction furnace and reducing them by heating. I have. In this publication, in order to maintain pellet strength and improve handling properties, the particle size is 6 to 30.
mm, and the iron oxide pellets dried until the water content becomes 1.0% by mass or less are disclosed, and reduced iron pellets are produced by heating the iron oxide pellets to 1100 to 1450 ° C. in a rotary hearth furnace. A method is disclosed.

Japanese Patent Application Laid-Open No. 10-147806: In this publication, iron-made dust is used as an iron source, and carbonaceous material is kneaded to form a raw pellet having a diameter of 6 to 18 mm (average diameter of about 10 mm). , And this is reduced to 12 by a rotary hearth type reduction furnace.
A method for producing granular reduced iron by firing at 50 to 1350 ° C is disclosed.

[0008] JP-A-11-193423 and 10
In Japanese Patent No. 147806, in consideration of handling and strength of pellets and briquettes, in order to prevent rupture due to rapid diffusion of moisture and volatile components inside the pellet, which is generally observed when a large diameter one is exposed to high temperature. The diameter of the pellet and the pre-dried state are devised.

In any case, in a known method including the above-mentioned technique, the raw material mixture is formed into a compact having a diameter of about 6 to 30 mm, generally about 10 mm or more, and this is heated and reduced. The method of heating and reducing by supplying it on the hearth of the furnace is adopted.
When exposed to a high temperature of about 1300 ° C. or higher at which the reduction reaction proceeds efficiently, the molded body is easily ruptured due to the effect of moisture and volatile components contained therein. After that, a method of charging into a heating reduction furnace is adopted.

[0010] In addition, large-diameter raw material compacts are generally difficult to granulate, which increases not only the costs required for granulation equipment and drying equipment, but also increases the production cost. Also, a binder is used to maintain the shape after drying stably, but if the blending amount of the binder is too large, the uniform dispersion of the iron oxide source and the carbon material in the formed body tends to be hindered, and heating is performed. There is a risk that the efficiency of the reduction reaction may be adversely affected. As described above, in some cases, drying may be omitted and the raw pellets may be supplied to the heating and reducing furnace in a raw pellet state. However, the raw pellets are not only low in strength, but also adhere to each other and adhere to a hopper of a supply device. Therefore, it is not a method suitable for practical use on an industrial scale because clogging is likely to occur and handling is poor.

As described above, when producing a reduced iron by heating and reducing a raw material compact containing an iron oxide source and a carbonaceous reducing agent,
Although the molded article has various problems due to its large diameter, most of the known methods use a raw material molded article having a diameter of 10 to 30 mm, which is a disadvantage due to the large diameter as described above. No active research has been done to solve the problem. In addition, as described above, some publications state that a molded article having a particle size in the range of 6 to 18 mm (average diameter of about 10 mm) is used, but as described above, a problem due to the large diameter is used. Attention has not been paid to reducing the particle diameter to less than 6 mm. In addition, when a raw material compact belonging to a small diameter of up to about 10 mm is used, how to control the conditions for producing reduced iron enables efficient solid reduction under stable operability. It cannot be said that sufficient research has been performed on whether reduced iron can be produced with high productivity.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to heat and reduce a raw material compact containing an iron oxide source and a carbonaceous reducing agent. In the production of solid reduced iron, the above-mentioned difficulties particularly caused by the size of the raw material compact, particularly the problems of molding or drying due to the large diameter, the problem of the strength of the compact, and the like are solved at once. Another object of the present invention is to establish a method capable of stably and efficiently performing drying and heat reduction from molding of a raw material molded body.

[0013]

Means for Solving the Problems A first structure according to the present invention which can solve the above problems is to form a raw material mixture containing a carbonaceous reducing agent and an iron oxide-containing substance, and reduce the formed body by heating. By heating in a furnace to reduce solid oxides of the iron oxide in the molded body to produce solid reduced iron, the gist is that a molded body having a particle size of less than 6 mm is used as a raw material molded body. ing.

[0014] A second structure according to the present invention is that a raw material mixture containing a carbonaceous reducing agent and an iron oxide-containing substance is similarly formed, and the formed body is heated in a heating reduction furnace to thereby form the formed body. When producing solid reduced iron by solid-reducing the iron oxide therein, while using a compact having a particle size of 10 mm or less as a raw material compact, the compact is placed on the hearth of the heating reduction furnace, The gist lies in that the heating reduction is carried out by charging so that the number of layers (H) satisfies the relationship of the formula [I]. H = Z.times. [X.times. (G / P)] / [A.times.LOAD@T]... [I] In the formula, H is the number of stacked compacts to be charged, and X is the production capacity specific to the heating reduction furnace. (Kg / min), Z is 0.7 to 1.3.
A is the hearth area (m ² ) in which the raw material compact is charged, LOAD is the mass per unit area (kg / m ² ) when the raw material compact is laid one layer on the hearth, G /
P represents the mass ratio of the charged amount of the raw material compact to the discharged reduced iron. T represents the production time (min) of the production capacity (X).

In practicing the first invention,
It is preferable to stack the raw material compacts in two to five layers on the hearth so that the productivity as product reduced iron can be sufficiently increased. More preferably, the particle size of the molded article when performing this method is 3 mm or more and less than 6 mm, but may be less than 3 mm depending on the operating conditions. If the green body is used, even if the raw material green body is not dried but is charged into a heating reduction furnace in an undried or semi-dry state, the green body does not burst or crush, and stable operation is possible. It is possible to efficiently produce reduced iron under the following conditions. When a raw material compact having a particle size of less than 3 mm is used, it is desirable to load the compact with three or more layers in order to enhance productivity.

In the second aspect of the present invention, as described above, the upper limit of the particle size of the raw material compact is increased to 10 mm, and
The number of layers (H) of the raw material compacts to be charged on the hearth so as to satisfy the relationship [I] is specified. As long as the relational expression is satisfied, the particle size of the raw material compacts is 6 to Even in the range of 10 mm, the productivity of reduced iron can be significantly increased as compared with the conventional method. In this case, the raw material compact preferably has a narrow particle size distribution, and preferably has a particle size of ± 3.
mm, more preferably ± 2 mm, since it is possible to further improve the operation stability and the productivity as reduced iron, and thus it is preferable.

In carrying out the first and second methods, in each case, after the raw material compact is charged into the heating reduction furnace, the surface temperature is reduced by １ ／ of the total reduction time. 120
By raising the temperature to 0 ° C. or higher, solid reduction can be efficiently performed in a short time, which is preferable. Also, a method in which carbonaceous powder is adhered to the surface of the raw material compact and charged into a heating reduction furnace By adopting the method, the erosion of the hearth refractory due to the molten slag generated in the solid reduction process derived from the gangue components in the raw material is suppressed, and the reoxidation of the reduced iron in the final stage of the solid reduction is also prevented. This is preferred. Further, in the present invention, by using a small-diameter raw material compact having a higher crushing strength than a large-diameter compact, the compact is placed on the hearth so as to have, for example, 3 to 5 layers in number of layers. Heat reduction can be promoted at a stretch, thereby increasing productivity. At this time, by forming peaks and valleys on the surface of the raw material molded body layer charged on the hearth to form irregularities, heat from above is further increased by increasing the effective heat transfer surface area of the molded body layer. It is preferable because the heat can be efficiently transmitted to each raw material molded body, and heat transfer to the lower raw material molded body can be accelerated, so that productivity can be further increased.

[0018]

DETAILED DESCRIPTION OF THE INVENTION As described above, in the present invention, an iron oxide source such as iron ore or iron oxide or a partially reduced product thereof (hereinafter sometimes referred to as iron ore or the like) and a carbonaceous material such as coke or coal are used. When a raw material compact containing a reducing agent (hereinafter sometimes referred to as a carbon material) is heated and reduced to produce solid reduced iron, the raw material compact particularly has a particle diameter of less than 6 mm or 10 m
By using a compact having a small diameter such as m or less, it is possible to facilitate granulation, reduce the cost of granulation equipment, improve the granulation yield and shorten the granulation time,
Furthermore, by using a small-diameter molded body, many advantages as described below can be enjoyed.

I) Since the heat transfer to the inside can be enhanced, the solid reduction can proceed efficiently in a shorter time and the productivity of reduced iron can be increased. Ii) The binder can be formed by forming a small-diameter molded body. Can be reduced, whereby the iron oxide source and the carbonaceous material can be evenly dispersed in the molded body, which also effectively works to improve the reduction efficiency. Iii) A small-diameter molded body Thereby, the crushing strength of each individual product can be increased as compared with the large-diameter molded product, and particularly, the collapse and powdering of the molded product during solid reduction can be suppressed, so that the production yield of reduced iron can be improved. In addition, since the thickness of the stack charged into the hearth can be increased, this also contributes to an improvement in productivity.

In order to effectively exert the above-mentioned effects by using a small-diameter compact, the particle size of the compact should be 10 m or more.
m or less, more preferably less than 6 mm, and it is difficult for a large-diameter molded body having a diameter larger than this to exhibit the above-mentioned effects effectively. However, the particle size is less than 2 mm, especially 1 mm
In the following small-diameter molded products, not only is it easy to cause clogging due to sorting by a sieve or the like and the handling property is deteriorated, but also the finally obtained reduced iron has a small diameter and the subsequent handling becomes complicated. Therefore, it is preferable that the distance be 2 mm or more, more preferably 3 mm or more. However, when practicing the present invention, not all the compacts need to be within the above-mentioned preferred particle size range. Even if a small-diameter molded product slightly out of the range is contained (preferably about 40% or less in mass ratio), the above-described effects can be effectively exhibited as a whole.

In the present invention, the small-diameter molded product is obtained by agglomerating a mixture containing an iron oxide source and a carbonaceous reducing agent,
It is a general term for pellets, briquettes, etc., regardless of their names, and may contain a mixture of them alone, or a small amount of debris or powder broken in the transfer process, etc. . There is no particular limitation on the method for producing the small-diameter molded product, and a normal molding method using a pan-type granulator, a disk-type granulator, a drum-type granulator, or the like may be employed.

The iron oxide source used as a raw material of the compact has a broad concept including, for example, mill scale in addition to iron ore, and of course, may include blast furnace dust, electric furnace dust, steelmaking dust, and the like. Absent. In addition, carbonaceous reducing agent (carbon material)
There is no particular limitation on the type of coal powder, and it is also possible to use charcoal powder and the like in addition to the most common coal powder and coke powder. Examples of the binder that may be added as necessary include bentonite and starch, but of course there is no reason to be limited to these.

If such a small-diameter compact is used, it is not only possible to efficiently perform solid reduction according to a conventional method by charging the compact in a single-layer state on the hearth of a heating and reducing furnace, but also to have excellent crushing strength. Taking advantage of the characteristics, the productivity per unit hearth area is increased by stacking multiple layers on the hearth, preferably 2 to 5 layers when the particle size is 3 mm or more and less than 6 and 3 or more layers when the particle size is less than 3 mm. It becomes possible. However, if the lamination charging thickness is excessively large, the small-diameter molded body on the lower layer side of the lamination tends to be insufficiently heated and the efficiency of solid reduction tends to deteriorate. It is desirable to suppress the number to about 10 layers or less (about 100 mm in thickness).

The supply of the small-diameter compact to the hearth surface is not necessarily performed by a special method. For example, the compact is cut out by a hopper, a vibration feeder, a drum feeder, or the like, and a gutter, a pipe, or an inclined plate for guiding is used. It is sufficient to adopt a method of supplying by feeding.

When the small-diameter compact is charged in a multilayered state, peaks and valleys of an arbitrary shape are formed on the surface of the layer in the vertical and / or horizontal direction to form irregularities, and the heat transfer effective surface area is increased. It is desirable to increase the heating efficiency by burner heating from above or radiant heat by enlarging. It is effective to form irregularities on the surface of the laminate, since the heat transfer efficiency of the laminated lower layer portion to the small-diameter molded body can be increased. The preferred shape, size, pitch and the like of the irregularities cannot be uniformly defined because they vary depending on the thickness of the laminated layer, but are preferably 5 to 200 m in height (the distance between the top and bottom).
m, more preferably in the range of 10 to 100 mm. There is no particular limitation on the method of forming the irregularities, for example, a method of changing the charging amount from a plurality of supply ports in a width direction of the hearth, a charging method, a method of charging from an irregular hopper extending in the furnace width direction. It is possible to arbitrarily select and apply a method in which the thickness is changed and a method in which the unevenness is formed by tracing with a surface shaping member having the unevenness after being substantially horizontally inserted.

Since the small-diameter compact used in the present invention has a small diameter as described above, the crushing strength of each compact is relatively high. In addition, because heat transfer is fast, it is quickly dried by initial heating, so it is possible to supply it on the hearth in an undried state, but damage due to impact at the time of charging and lamination load is more. To ensure prevention, it is preferable that at least the surface layer side of the small-diameter molded body is previously dried and then charged, so that clogging in a charging hopper or the like due to adhesion of the small-diameter molded body can be prevented. preferable.

Further, in practicing the present invention, a method in which the carbonaceous powder is attached to the surface of the small forming body and then charged on the hearth may be employed. The degree of reduction of the atmosphere gas in the vicinity of the small-diameter compact is increased so that the solid reduction proceeds more efficiently.b) The insufficient carbonization of the lower layer, which tends to occur when small-diameter compacts are stacked and charged, is compensated by the carbonaceous powder. C) acts on FeO, which is likely to be caused by insufficient reduction in the lower layer, and reduces it promptly, so that the production of FeO-containing molten slag that significantly damages the hearth refractory is also reduced. (2) If the carbonaceous powder is adhered to the surface of the small-diameter molded body by dusting it, mutual adhesion and adhesion to the charging hopper etc. can be prevented. , The small-diameter compact in the undried state It is particularly useful for entering.

As the carbonaceous powder used here, coal powder, coke powder, charcoal powder and the like are arbitrarily selected and used. When the carbonaceous powder is to be adhered to the surface of the small-diameter molded body, a method of attaching the carbonaceous powder to the surface, or a method of dispersing the carbonaceous powder in a dispersion medium such as water and spraying the dispersion may be adopted.

In the present invention, the particle size is 10 mm or less, especially 6 mm.
The requirement of the above-mentioned formula [I] added when a small-diameter compact of 10 mm to 10 mm is used is based on the production capacity (X) inherent in the heating reduction furnace to be used, and then the raw compact which is stacked and charged is taken into account. And the reason why the formula [I] is determined is as follows.

That is, the production amount of reduced iron is determined by the production capacity per unit time (X: kg / min) specific to the heating reduction furnace, by the hearth area (the hearth area of the portion where the raw material compact is charged:
m ² ) is (A), and the charged amount of the raw material compact per unit time and unit area (kg / min · m ² ) is (B).
It is represented by the following formula [II]. X = A × B [II] However, the iron oxide in the raw material compact is reduced to Fe by heat reduction, the carbon material is decomposed, and volatile components such as Zn and Pb are diffused. Since the particles are also scattered by powdering, the mass ratio (G /
When P) is added and corrected, the following equation [III] is derived. X = A × B / (G / P) ... [III] Here, the charged amount (B) of the raw material molded body is the mass per unit area (kg) when the raw material molded body is laid one layer on the hearth.
/ M ² ) is (LOAD), the number of layers is (H), and the production time (min) of the production capacity (X) is (T), which can be expressed by the following formula [IV]. formula
Substituting into [III], the following equation [V] is derived. B = LOAD × H ÷ T... [IV] X = [A × LOAD × H ÷ T] / (G / P)... [V] Then, the above formula [V] is modified to obtain the number of layers (H). The following formula [VI] can be derived by changing the calculation formula into H = [X × (G / P)] / [A × LOAD @ T]... [VI]

Here, assuming that the charging amount per unit area is ideal, the weight per unit area when one layer of the raw material molded article is laid, and (G / P) is (raw material) Since this is the mass ratio of the compact / product reduced iron), the ideal number of layers (H) is determined from these values. However, in practice, there are considerable variations in the heating conditions and reducing atmosphere conditions due to the characteristics specific to the heating and reducing furnace, and therefore, it is necessary to make corrections taking into account the production conditions specific to the practical furnace, and the (H) variation is required. Was confirmed in a practical furnace, the variation (Z) was in the range of ± 30%, that is, in the range of 0.7 to 1.3, and as shown before, it was as shown in the following formula [I]. It was confirmed that. H = Z × [X × (G / P)] / [A × LOAD @ T]... [I]

Next, a specific apparatus for producing reduced iron by performing solid reduction using the small-diameter compact as a raw material will be briefly described.

FIG. 1 is a schematic plan view showing an example of a moving hearth type (in this example, a rotary hearth type) reduction furnace to which the present invention is applied.
A cover for covering the furnace body is omitted in the drawing. 1 is a doughnut-shaped rotary hearth, 2 is a raw material charging section, 3 is a surface shaping member,
Reference numeral 4 denotes a cooling unit, 5 denotes a reduced iron discharging device, and 6 denotes a burner for heating.

When producing reduced iron using this apparatus, a raw material compact containing an iron oxide source and a carbon material is charged into the raw material charging section 2.
From above to the rotary hearth 1 so as to have an appropriate thickness (number of layers). For the charging of the raw material molded body, the raw material molded body is cut out with, for example, a hopper, a vibration feeder, a drum feeder, or the like, and the charging amount is adjusted using a guide pipe or an inclined plate. Then, the surface of the raw material charging layer is smoothed and smoothed by the surface shaping member 3 immediately downstream of the raw material charging section 2, but at this time, the surface of the raw material charging layer is appropriately adjusted by the surface shaping member 3 as described above. It is preferable to form irregularities with a proper height and pitch because the efficiency of heat transfer of burner heating and radiant heat to the raw material molded body layer can be increased.

The charged raw material compact is placed on the rotary hearth 1
While being moved in the direction of arrow X by rotation,
Heated by the combustion heat and radiant heat from the burner 6
Body reduction is promoted. This heating includes heavy oil, pulverized coal,
Burner heating using plastic or other fuel
Combustible gas (CO,
H _Two) To combust air and oxygen by effectively utilizing
Heat, or heat storage type heating, either individually or appropriately.
Any combination can be adopted. Generated by reduction
CO_TwoAnd flue gas from the exhaust port (not shown).
Will be issued.

Then, the solid reduction is completed (90% by metallization ratio).
The reduced product thus cooled is cooled by a cooling unit 4 (for example, a water-cooled jacket provided at the lower part of the hearth or spraying a cooling gas), and is sequentially taken out of the furnace by an optional discharge device 5. The configuration of the discharge device is not particularly limited, and a method using a screw or a scraper, a method using gas blowing or suction to discharge, and the like can be arbitrarily selected and adopted.

When the temperature at the time of the above-mentioned heat reduction (solid reduction) is too high, specifically, at a certain time during the solid reduction process,
When the ambient temperature becomes higher than the melting point of the slag composition composed of gangue components and unreduced iron oxide in the raw material, these low-melting slags melt and react with the refractories constituting the moving hearth to melt. Damage, and it becomes impossible to maintain a smooth hearth. Also,
When heat more than required for the reduction of iron oxide is applied during the solid reduction period, FeO which is an iron oxide in the small-diameter compact is melted before being reduced, and the molten FeO becomes carbon ( So-called smelting reduction (a phenomenon in which reduction proceeds in a molten state, which is different from solid reduction) that reacts with C) proceeds rapidly. Although metallic iron is also generated by the smelting reduction, when the smelting reduction occurs, the highly fluid FeO-containing slag remarkably dissolves the hearth refractory, making continuous operation as a practical furnace difficult.

Such a phenomenon varies depending on the iron ore and the carbonaceous material constituting the small-diameter compact or the composition of the slag-forming component contained in the binder and the like. However, the ambient temperature at the time of solid reduction exceeds about 1500 ° C. Irrespective of brands such as raw iron ore and the like, the above-mentioned undesired smelting reduction reaction proceeds and the erosion of the hearth refractory becomes remarkable. It is desirable to suppress it. However, if the heating temperature is too low, the progress of solid reduction becomes slow.
The temperature is desirably set to 00 ° C. or higher, more preferably 1300 ° C. or higher.

Then, the raw material compact charged in the furnace is
In order to efficiently promote the reduction rate without causing partial melting of the slag component contained in the molded body while maintaining the solid state, the furnace temperature is set to 1200 to 1500 ° C, more preferably 1250 to 1450 ° C. It is preferable to perform the solid reduction while keeping the temperature within the range, and more preferably to raise the temperature to 1200 ° C. in about 1/3 of the time required for the total reduction in the furnace. The solid reduction can be almost completed by heating for about a minute.

Incidentally, in the heating reduction furnace used in the practice of the present invention, burner heating is often employed for heating the raw material compact. In this case, in the initial stage of the solid reduction, a large amount of CO gas is generated due to the reaction between the iron oxide source and the carbon material in the raw material compact charged in the furnace, and the vicinity of the raw material compact is released from itself. A high reducing atmosphere is maintained by the shielding effect of the CO gas.

However, during the latter half of the solid reduction, the self-shielding effect is reduced due to a rapid decrease in the amount of generated CO gas, and the combustion exhaust gas (oxidizing gas such as CO ₂ or H ₂ O) generated by the burner heating is reduced. Gas), and the reduced iron that has been reduced is more likely to be re-oxidized. As a preferable means for efficiently promoting the solid reduction while suppressing such re-oxidation as much as possible, there is exemplified a method in which carbonaceous powder is previously attached to the surface of the raw material compact as described above. That is, if the carbonaceous powder is attached to the surface of the raw material compact in such a manner, the carbonaceous powder may be oxidized gas (CO ₂ CO ₂₎ generated by burner combustion in the latter half or late stage of solid reduction.
And H ₂ O) to convert these gases into reducing gases such as CO and H ₂ , so that the vicinity of the reduction products that have undergone solid reduction can be maintained in a highly reducing atmosphere, and reduced iron Can be prevented as much as possible. In order to effectively exhibit such a reoxidation preventing effect, the carbonaceous powder is preferably 2 mm or less, more preferably 1.0 m or less.
It is desirable that fine carbonaceous powder of m or less be adhered. Examples of a method of attaching the carbonaceous powder include a method of attaching the carbonaceous powder to the surface of the raw material compact in an undried state, and a method of attaching the carbonaceous powder by spraying using a dispersion medium such as water. However, of course, it is not limited to these methods. If the carbonaceous powder is adhered to the surface of the raw material molded body in this way, as another additional effect, the adhesion between the molded bodies and the raw material when the raw material molded body is charged onto the hearth in an undried state. It is preferable because the adhesion to the charging hopper is also suppressed, and the raw material is smoothly charged.

[0042]

EXAMPLES Hereinafter, the structure, operation, and effects of the present invention will be described in detail with reference to examples. However, the present invention is not limited to the following examples, and can be adapted to the above and following points. The present invention can be implemented by appropriately changing the scope, and all of them are included in the technical scope of the present invention.

Example 1 The following two types of mixtures were used as raw materials, and several types of compacts having different particle sizes were manufactured using a pan-type granulator, and each of them was ± 10% of the target particle size. When the productivity of the granulated product within the range was compared, the result shown in FIG. 2 was obtained. Raw material 1 Iron oxide source (iron ore) composition: Fe: 68.8%, Si
O ₂ : 2.1%, Al ₂ O ₃ : 0.6%, particle size: 75 μm
The following carbon material (coal powder) composition: fixed carbon; 72.2%, volatile matter;
18.4%, ash content: 9.4%, particle size: 75 μm or less Iron ore / coal powder / binder mixing ratio: 78.3% / 20
% / 1.7% Raw material 2 Iron oxide source and carbon material (blast furnace dust) composition: Fe; 3
_{8.02%, SiO 2; 2.51%} , Al 2 O 3; 1.0
3%, fixed carbon: 14.57%, particle size: 75 μm or less Blast furnace dust / binder mixing ratio: 98% / 2%

As is apparent from FIG. 2, the absolute value of the granulation productivity varies considerably depending on the type of the raw material. In any case, the larger the target particle size of the granulated product is, the lower the granulation productivity is. In particular, when the target particle size exceeds 10 mm, the granulation productivity is significantly reduced. And the target particle size is 10 mm
In the following, it can be confirmed that particularly when the thickness is less than 6 mm, a high granulation productivity can be stably obtained. That is, a small-diameter molded product having a particle diameter of 10 mm or less, more preferably less than 6 mm, as defined in the present invention, can obtain higher granulation productivity than a conventionally used large-diameter molded product, The advantage is exerted effectively in the body manufacturing stage.

Example 2 For two types of compacts having a particle size of 5 mm and 18 mm produced using the same raw material as the raw material 1 of the above-mentioned Example 1, an undried product and a dried product were prepared, and each was placed in an experimental furnace. The presence or absence of explosion when the temperature was increased to 1350 ° C. at a rate of 1350 ° C./min after charging was compared. The presence or absence of explosion was determined by the fact that a part of the molded body burst when the above-mentioned heating was performed in the furnace and the spherical shape could not be maintained for more than half.

The results are as follows. In the case of a dry molded article, no explosion occurred in any of the specimens having a particle size of 5 mm or 18 mm, but in the undried molded article, the difference depending on the particle size was remarkably exhibited. A 5 mm one does not explode at all, whereas a large diameter 18 mm molded article has exploded 90%, which is evident to have a significant adverse effect on solid reduction. Molded particle size 5mm 18mm Dry molded body 0/10 0/10 Undried molded body 0/10 9/10

Example 3 Molds having various particle diameters were manufactured using the dust used as the raw material 2 in the above example, and each compact was subjected to a reduction experiment (sample molding) using an experimental furnace (box-type electric furnace). The body was placed in a flat plate made of refractory, and the effect of the particle size of the formed body and the number of layers (1 to 5 layers) in each furnace on productivity was examined. The productivity was determined based on the reduction time required until the reduction rate of each sample compact reached 90%. The reduction conditions employed in this experiment were all nitrogen gas atmosphere and the temperature was constant at about 1300 ° C.

The results are shown in FIGS. 3 and 4. The effect of the layer thickness of the molded product having a particle size exceeding 6 mm on the productivity is as follows.
The layer thickness is divided into a group of 1 and 2 layers and a group of 3 to 5 layers. When the layer thickness is one or two, since the molded body receives sufficient radiant heat and the entire layer is quickly heated and heated, the productivity is improved as the particle diameter of each molded body is increased. . On the other hand, when the layer thickness is three or more, transmission of radiant heat to the lower-layer-side molded body is delayed, so that productivity as a whole has leveled off. That is, if the particle size of the raw material compact is 6 mm or more, especially more than 10 mm, the influence of insufficient heat transfer on the lower layer due to the multi-layer lamination is remarkably exhibited, which hinders the improvement of productivity. It can be seen that if the diameter is suppressed to 10 mm or less, productivity can be significantly increased by increasing the weight of the raw material molded body with the increase in the number of laminations (FIG. 3).

In particular, when a compact having a particle size of less than 6 mm is used (FIG. 4),
The group in which the number of layers is increased to 3 to 5 layers clearly shows higher productivity. That is, in order to more efficiently increase the productivity by increasing the weight of the raw material compact due to the increase in the number of layers, it can be confirmed that it is extremely effective to make the particle size of the compact less than 6 mm. This is presumably because the packing density of the raw material packed layer was increased by reducing the particle size of the compact, and the difference in heat transfer rate was compensated for, so that the temperature could be rapidly raised to the lower layer. Therefore, if a small-diameter molded body is used, the productivity can be increased by increasing the amount of charge per unit hearth area by increasing the number of layers.

In the same manner as described above, heat reduction experiments were conducted by laminating 1 to 5 layers of molded articles having different particle diameters, from the start of heating until the metallization ratio of each molded article reached 90%. By measuring the required time, the optimum layer thickness according to the particle size of the molded article was examined. As a result, the particle size is 10 mm
In the molded article of No. 1, the optimum layer thickness is 1.1 layers, 2.0 layers when the particle diameter is 8 mm, 1.7 layers when the particle diameter is 6 mm, 2.7 layers when the particle diameter is 4 mm, and 3.0 layers when the particle diameter is 3 mm. 2 layers, particle size 2mm
Was confirmed to be 4.3 layers.

FIG. 5 is a graph showing the results of the above experiment. In consideration of the characteristics of the practical furnace and the variation in productivity, the optimum value corresponding to the particle size of the compact within the shaded area in FIG. By setting the number of stacked layers, the productivity per unit hearth area can be effectively increased. Also, as is clear from this graph, the particle size of the molded product is 10 mm or less,
More preferably, when the thickness is set to less than 6 mm, particularly in the range of 2 to 5 mm, the optimum number of laminations can be increased, and the productivity per unit hearth area can be effectively increased.

When LOAD (kg / m ² ) in the above formula [I] is obtained by setting the particle size of the molded body to D (mm), the following formula is obtained. LOAD (kg / m ² ) = apparent density (kg) / m ³ ) × 3/4 ・ π (D / 2) ² (m
³ ) Since ΔD ² LOAD is substantially determined by the particle size (D) of the compact, as a result, as shown in FIG. ). In addition, the particle diameter here, when the particle diameter of the raw material molded article is substantially uniform, adopts the diameter, when the particle diameter is non-uniform or the shape is also non-uniform like briquettes, weight average or The average diameter converted into a sphere may be used.

[0053]

The present invention is constituted as described above. When a mixture containing an iron oxide source and a carbonaceous reducing agent is formed, and the mixture is heated and solid-reduced to produce reduced iron, the raw material is reduced. By using a small-diameter molded body of 10 mm or less, more preferably less than 6 mm as a molded body, the above-mentioned difficulties derived from the size of the raw material molded body, particularly problems in molding or drying due to the large diameter, The problem of the strength of the molded body, the problem of insufficient heat transfer on the lower layer due to the charging of the laminated body, etc. are solved at once, and a series of processes from molding of the raw material molded body to drying and solid reduction by heating are stably and efficiently performed. I got it.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating a heat reduction facility used in the present invention.

FIG. 2 is a graph showing the relationship between the particle size of a raw material compact and granulation productivity.

FIG. 3 is a graph showing the effect on productivity when the number of layers is changed for each particle size of a raw material compact.

FIG. 4 is an enlarged graph showing a small particle size side having a particle size of 6 mm or less in FIG. 3;

FIG. 5 is a graph showing the relationship of the optimum number of layers according to the particle size of the raw material compact.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Rotary hearth 2 Raw material charging part 3 Surface shaping member 4 Cooling part 5 Discharge device 6 Combustion burner

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) C22B 1/245 C22B 1/245

Claims (13)

[Claims] 1. A raw material mixture containing a carbonaceous reducing agent and an iron oxide-containing substance is formed, and the formed body is heated in a heating reduction furnace, whereby iron oxide in the formed body is solid-reduced. In producing iron, the raw material compact has a particle size of 6
A method for producing reduced iron, comprising using a molded product having a diameter of less than 1 mm. 2. A raw material mixture containing a carbonaceous reducing agent and an iron oxide-containing substance is formed, and the formed body is heated in a heating reduction furnace so that iron oxide in the formed body is solid-reduced. In producing iron, the raw material compact has a particle size of 1
Using a compact having a size of 0 mm or less and loading the compact on the hearth of the heating and reducing furnace so that the number of layers (H) that satisfies the relationship of the following formula [I] is obtained. Iron manufacturing method. H = Z × [X × (G / P)] / [A × LOAD @ T]... [I] In the formula, H is the number of stacked compacts to be charged, and X is the specific production capacity of the heating reduction furnace. (Kg / min), Z is a positive number in the range of 0.7 to 1.3, A is a hearth area (m ² ) in which the raw material compact is charged, and LOAD is 1 The mass per unit area (kg / m ² ) when the layers are spread, G / P is the charged amount of the raw material compact, and the mass ratio T of the reduced iron discharged is the production capacity (X) production capacity. Time (min) respectively. 3. The raw material compact has a particle size of 3 mm or more and 6 m or more.
2. The method according to claim 1, wherein the number is less than m. 4. The method according to claim 3, wherein the raw material compacts are stacked and charged in two to five layers on a hearth. 5. The method according to claim 1, wherein the particle size of the raw material compact is less than 3 mm. 6. The method according to claim 5, wherein the raw material compacts are stacked and charged in three or more layers on a hearth. 7. The method according to claim 1, wherein the raw material compact is charged into a heating reduction furnace without drying. 8. The raw material molded body has a particle size of 6 to 10 mm, and the molded body is charged on a hearth in one to three layers.
Production method described in 1. 9. The method according to claim 8, wherein the particle size of the raw material compact is homogenized to within ± 3 mm. 10. After the raw material compact has been charged into a heating and reducing furnace, the surface temperature is reduced to 12/3 of the total reduction time.
The method according to any one of claims 1 to 9, wherein the temperature is raised to 00C or higher. 11. The method according to claim 1, wherein carbonaceous powder is attached to the surface of the raw material compact and charged into a heating reduction furnace. 12. The raw material compact charged on the hearth,
The method according to any one of claims 1 to 11, wherein the number of layers is equalized so as to be 3 to 5 layers. 13. The method according to claim 1, wherein peaks and valleys are formed on the surface of the raw material layer loaded on the hearth.